1. Field of the Invention
The present invention relates to a chuck and a tube joint. In particular, the present invention relates to a tube joint and a chuck preferable to facilitate the improvement in productivity of the tube joint and the realization of a compact size and a light weight of the tube joint.
2. Description of the Related Art
In general, as shown in FIG. 15, for example, a tube joint comprises a tubular first tube joint member 300, a tubular second tube joint member 302 to be coupled to the first tube joint member 300, a sleeve 304 attached to a coupling portion between the first and second tube joint members 300, 302, for coupling and releasing the first and second tube joint members 300, 302, a compressive coil spring 306 for urging the sleeve 304 in a direction to couple the first and second tube joint members 300, 302 to one another, and a plurality of balls 308 for engaging the first and second tube joint members 300, 302 with each other.
The first tube joint member 300 includes a cylindrical member 312 which has its front portion to be inserted into the sleeve 304 and which has a female screw 310 threaded on its rear portion, and a coupling member 314 having a cylindrical configuration which is screwed into the female thread of the cylindrical member 312. An accommodating space 318 for accommodating a valve plug 316 is formed at a front portion of the coupling member 314. A closing plate 324, which is provided with a slit 322 for inserting a part of the valve plug 316, is installed between the cylindrical member 312 and the coupling member 314. A compressive coil spring 328 is inserted into the accommodating space 318, for always urging the valve plug 316 in the direction toward the closing plate 324 to close the slit 322 with a flange 326 of the valve plug 316.
The sleeve 304 is installed such that its end surface 304a is flushed with an end surface 312a of the cylindrical member 312 of the first tube joint member 300. The sleeve 304 is always urged resiliently by the compressive coil spring 306 in the direction to make separation from the first tube joint member 300 toward the second tube joint member 302. However, the sleeve 304 is suppressed so that it is not disengaged from the first tube joint member 300, by the aid of a ring-shaped stopper member 330 which is installed in the vicinity of the end surface 312a of the cylindrical member 312.
The cylindrical member 312 of the first tube joint member 300 has a plurality of holes 332 which are formed at its front end portion (portion overlapped with the second tube joint member 302), the holes 332 being formed at positions disposed at equal intervals along the circumferential direction of the cylindrical member 312. The diameter of each of the holes 332 is reduced toward the central axis of the cylindrical member 312, and the balls 308 are inserted into the holes 332 respectively. The ball 308 is arranged such that a part of the ball 308 is inserted into and engaged with an annular groove 334 formed on the surface of the second tube joint member 302, when the second tube joint member 302 is inserted into the hollow portion of the cylindrical member 312. FIG. 15 is illustrative of a case in which only two of the holes 332 and the balls 308 are shown respectively.
Usually, the balls 308 are pressed toward the central axis of the cylindrical member 312 by the aid of the sleeve 304. However, when an external force is applied to the sleeve 304 to move the sleeve 304 toward the coupling member 314 along the axial direction of the first tube joint member 300, the balls 308 are released from the pressing action of the sleeve 304. In this situation, the valve plug 316 is operated such that the flange 326 thereof abuts against the closing plate 324 to close the slit 322 by being urged by the compressive coil spring 328. Thus, the valve plug 316 is in the closed state.
Starting from this stage, when the second tube joint member 302 is inserted into the hollow portion of the cylindrical member 312 of the first tube joint member 300, the valve plug 316 is moved rearwardly against the urging force of the compressive coil spring 328 by means of the end surface of the second tube joint member 302. Thus, the valve plug 316 is in the open state.
When the external force applied to the sleeve 304 is removed, the sleeve 304 is resiliently urged in accordance with the elastic restoration of the compressive coil spring 306. Accordingly, the sleeve 304 is restored to the position at which the end surface 304a of the sleeve 304 is flushed with the end surface 312a of the cylindrical member 312.
In this state, the balls 308 are pressed by the sleeve 304 again toward the central axis of the cylindrical member 312. As a result, the balls 308 are engaged with the annular groove 334 provided on the second tube joint member 302.
The engagement of the balls 308 disables the second tube joint member 302 from being disengaged from the first tube joint member 300. Therefore, the first and second tube joint members 300, 302 are tightly joined to one another.
When the tube joint as described above is produced, an inconvenience arises in that the production cost cannot be made inexpensive, because the production steps are complicated.
The inconvenience will be specifically explained below. As described above, the conventional tube joint comprises the four balls 308, and the sleeve 304 for pressing the balls 308 toward the central axis of the tube joint. When such a tube joint is assembled, complicated operations must performed, including (1) formation of the holes 332 of the cylindrical member 312 for constructing the first tube joint member 300, (2) insertion of the balls 308 into the holes 332, and (3) installation of the sleeve 304 while pressing the balls 308 by using a jig so that the balls 308 are not disengaged from the holes 332. Further, it takes a long period of time to perform the operations.
The cylindrical member 312 and the coupling member 314 of the first tube joint member 300 are mutually different members, and it is also complicated and troublesome to connect them to one another (by means of screwing operation). Therefore, it is not easy to improve the production efficiency of the tube joint, resulting in the increase in the production cost of the tube joint.
It has been hitherto demanded for the tube joint to have a compact size and a light weight because of the following reason. That is, if the tube joint has a large size, the degree of freedom is restricted for the arrangement of the tube. Further, when the tube joint is connected with the tube, then the tube joint interferes with, for example, another tube and equipment, and it is difficult to perform the connecting operation in some cases. In the latter case, there is a likelihood that the connection between the tube and the tube joint may be incomplete, and it is feared that the sealing performance may be insufficient.
If the tube joint has a large weight, the tube connected with the tube joint may be bent due to the weight of the tube joint. In this case, it is also feared that the connection between the tube and the tube joint may be incomplete, and it is impossible to obtain any sufficient sealing performance.
In the case of the conventional tube joint as described above, it is necessary to provide a sufficiently long size of the first tube joint member 300, especially of the cylindrical member 312 along the axial direction, in order to ensure the space for inserting the balls 308. Further, the coupling member 314 is coupled by being screwed to the rear portion of the cylindrical member 312. Therefore, the length of the tube joint along the axial direction is necessarily increased, and hence the weight is also increased in accordance therewith.
Further, it is demanded to obtain a large flow rate of the fluid, for the tube joint which is provided with the valve plug 316 at its inside. In order to realize the large flow rate, it is effective to enlarge the inner diameter of the tube joint. In the case of the conventional tube joint, it is conceived to thin the wall thickness of the cylindrical member 312 of the first tube joint member 300. For this purpose, it is necessary to decrease the diameter of the balls 308. However, if the diameter of the balls 308 is decreased, the balls 308 are insufficiently engaged with the annular groove 334. As a result, it is feared that the second tube joint member 302 may be easily disengaged from the first tube joint member 300. Therefore, in the case of the conventional tube joint, it is not easy to contemplate the large flow rate as well.